Recovery of color-forming couplers

ABSTRACT

THE SEPARATION OF 2,4-BIS(BENZENESULFONAMIDO)PHENOL BALANCING DEVELOPING AGENT FROM N-(O-ACETAMIDO PHENETHYL)-1-HYDROXY-2-NAPHTHAMIDE COLOR-FORMING COUPLER IS ACCOMPLISHED BY TECHNIQUES EMPLOYING AN OXIDIZING AGENT, ADVANTAGEOUSLY SUPPLIED BY AERATION, IN STRONGLY ALKALINE SOLUTIONS CONTAINING THE COUPLER AND BALANCING DEVELOPING AGENT, SEPARATING RESULTING SOLIDS FROM THE SOLUTION, AND LOWERING THE SOLUTION PH TO PRECIPITATE THE COUPLER.

United States Patent 3,655,753 RECOVERY OF COLOR-FORMING COUPLERS Austin C. Cooley, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N .Y. N0 Drawing. Filed Oct. 2, 1969, Ser. No. 863,324 Int. Cl. C07c 103/26 U.S. Cl. 260559 R 9 Claims ABSTRACT OF THE DISCLOSURE The separation of 2,4-bis(benzenesulfonamido)phenol balancing developing agent from N-(o-acetamido phenethyl)-l-hydroxy 2 naphthamide color-forming coupler is accomplished by techniques employing an oxidizing agent, advantageously supplied by aeration, in strongly alkaline solutions containing the coupler and balancing developing agent, separating resulting solids from the solution, and lowering the solution pH to precipitate the coupler.

This invention relates to the separation of cyan colorforming couplers from solutions containing the couplers and acid insoluble phenolic developing agents. In one of its aspects this invention relates to the recovery of colorforming couplers from used color developer solutions from photographic color development processes. In another of its aspects the present invention relates to the separation of acid insoluble cyan color-forming couplers from color developing solutions which contain the coupler and acid insoluble, phenolic, competing developing agents, which solutions have been used for dye-forming development in processing multicolor photographic elements.

Alkaline solutions containing color developing agents and color-forming coupling agents are commonly utilized in photographic processing, especially reversal color processing. In the processing of three color type photographic elements, for example, the final picture is normally made by the formation of a cyan dye image, a yellow dye image, and a magenta dye image in superposed relationship. Reversal processing, for example, of multilayer color film of the type containing no incorporated couplers, involves black-and-white development of the image exposed element followed by reversal re-exposures and development in color developers containing the desired color developing agent and color forming coupler. The cyan dye image development is thus accomplished with an alkaline developer solution which contains color developing agent and a cyan-forming color coupler. Where reversal exposed silver halide in the yellow sensitized layer is developed to silver, the color developing agent couples with the cyan-forming coupler to form a nondiffusing dye image. The yellow and magenta dye layers are developed analogously using yellow and magenta color-forming couplers.

In addition to the color developing agent and colorforming coupler, the alkaline developer solution usually contains other constituents such as potassium bromide, sodium sulfite, sodium carbonate, and advantageously competing developing agents inorder that. the development can result in an image having the desired sensitometric characteristics. One type of competing developing agent which has been found to give exceptional results in such systems is 2,4-bis(benzenesulfonamido)phenol as described in Bard, U.S. application Ser. No. 801,138, filed Feb. 20, 1969 and now U.S. 3,592,652, which is a continuing application of U.S. application Ser. No. 639,274, filed May 18, 1967 and now abandoned.

When the concentration of any important component of the developer solution, for example, as in a spent developer, falls outside the precise concentration range 3,655,753 Patented Apr. 11, 1972 set for that system, the continued use of such material would result in faulty development and developed images having poor sensitometric properties. To compensate for this, the developer is replenished, as in a continuous system in which case there is washover which ordinarily is discarded, or the entire developer is discarded so that the processor can start with fresh developer, as in a batch system. In either case, the used or exhausted developer normally contains some of the original components of the developer. For example, the color-forming coupler is frequently present in substantial concentration. Because such couplers are relatively costly, it is desirable to recover them for reuse in fresh developer solution.

Several methods for recovery of color-forming couplers have been known and are described in Anselm and Reitz, U.S. Pat. No. 3,458,574, issued July 29, 1969. One of the purification methods described in that patent involves precipitating acid insoluble color-forming couplers from the aqueous alkaline developer by lowering the pH, e.g., with carbon dioxide, separating the precipitate from the solution, e.g., by filtering or centrifuging, washing the coupler, and then drying.

Although such methods have enjoyed varying degrees of success in most systems, it has been found that when the developer contains a N-(o-acetamido phenethyl)-1- hydroxy 2 naphthamide cyan color-forming coupler and a 2,4-bis(benzenesulfonamido) phenol competing developing agent, the prior art systems will not give the purity desired for use in many photographic systems. The methods evidently will separate the coupler and competing developing agent from many of the other contaminants present in the developer system but do not effect an efficient separation of the coupler from the competing developing agent.

I have found that N-(o-acetamido phenethyl)-l-hydroxy 2 naphthamide couplers can be separated from the mixtures containing the coupler and 2,4-bis(benzenesulfonamido)phenol competing developing agents by methods which include oxidation of the balancing developing agent in the presence of strong alkali.

According to one advantageous embodiment of the present invention a color developer solution having a pH of at least about 10, and usually above about 12, and containing N-(o-acetamido phenethyl) 1 hydroxy-2- naphthamide color forming coupler and 2,4-bis(benzene sulfonamido) phenol is treated to lower the pH of the solution whereby the coupler and balancing developing agent precipitate. The precipitate is then separated from the remaining solution, e.g., by centrifuging or filtering, and redissolved in strong alkali, e.g., pH at least 10 and desirably at least about 12. The aqueous alkali solution is then contacted by oxidizing agent whereby the competing developer is converted to reaction products which are insoluble at high pH, e.g., above 10, and/or products which are acid soluble. At this point it is again desirable to separate any precipitate which may be present from the remaining solution, e.g., again by filtering or centrifuging the pH of the solution is then lowered whereby the coupler precipitates, e.g., at pH below about 9, desirably about 7-8. The precipitated coupler can then be separated with an appropriate filter or centrifuge. Washing each of the coupler-containing precipitates is usually advantageous.

Following such a procedure results in couplers which can normally be safely used in high-quality photographic processing either with or without blending with freshly synthesized coupler. In some instances it may, however, be desirable to further purify the coupler in which case other purification methods, for example, described in U.S. Pat. No. 3,458,574, may be utilized in conjunction with the oxidation method. If another purification svsmm is employed after the oxidation method, the last separation step of the oxidation method can include the additional system, e.g., a separate filtration would not have to precede a method as described and claimed in U.S. 3,458,574. Also, in some instances it is advantageous to use the oxidation technique directly on the used developer. In this case, the method according to the present invention involves contacting the-high pH developer (above 10, desirably above about 12) with the oxidizing agent whereby the balancing developing agent is oxidized to high pH insoluble and/or acid soluble derivatives, removing suspended (e.g., precipitated) solids from the solution (e.g., by filtration or centrifuging), lowering the pH of the solution to precipitate the coupler, and separating the precipitated coupler from the solution (e.g., again by filtering or centrifuging). This abbreviated method can also be employed in conjunction with other purification techniques.

The oxidizing agent employed according to the present invention may vary widely. Strong oxidizing agents such as peroxide and persulfate can effectively be utilized, but weaker oxidizing agents can be employed. For example, oxygen supplied by aeration is especially useful in my method. The time the oxidizing agent is in contact with the solution can also vary widely depending upon the particular agent selected, the particular method of dispersion of the agent, the amount of balancing developing agent, the concentration of the developing agent, the degree of purification desired, the particular purification method chosen, the selected temperature (which also can vary widely), etc.

One simple method of determing how long the reaction should proceed or how much oxidizing agent should be employed, etc, it is to test a portion of the developing solution by known techniques, for example, by placing a small drop of the solution on a thin absorbent sheet and then spraying the damp area with a silver nitrate solution. If the spot turns black, balancing developing agent is still present. If the area doesnt darken when sprayed with silver nitrate, the developing agent has been completely oxidized. Chromatographic techniques may also be employed.

The oxidation method can be employed for effective separation of 2,4-bis (benzenesulfonamido)phenol balancing developing agent from N-(o-acetamido phenethyl)-lfhydroxy-Z-naphthamide cyan color forming coupler in many systems. It is especially useful in recovering the coupler from solutions which also include color developing agents, e.g., para-phenylenediamine developing agents as well as other acid soluble components. It is also useful for separation of simple mixtures of the coupler and balancing developing agent, e.g., an aqueous alkaline solution containing the two components.

The following examples are intended to illustrate my invention and advantages thereof.

EXAMPLE 1 Used color developer solution having a pH of about 12.5 and containing para-phenylenediamine developing agent (N,N-diethyl-p-phenylenediamine monohydrochloride), 2,4-bis(benzenesulfonamido)phenol balancing developing agent, sodium sulfite, and N- (o-acetamido phenethyl)-1-hydroxy-2-naphthamide is treated by bubbling CO into the solution to lower the pH to about 7.5. A precipitate containing balancing developing agent and coupler is formed and is collected by filtration. The procedure is repeated until about 50 kg. of damp precipitate (about 80% water) is collected. A 150 liter tank is fitted with a mechanical mixer and filled to about one-half level with water. The mixer is started and the damp precipitate is added slowly. Additional water is added as needed for mixing to almost 100 liters. After about 8 minutes of stirring 10 N sodium hydroxide is added until the solution pH is about 13.5 (about 5 /2 liters). Stirring is continued for about an hour until the precipitate is completely dissolved.

Air is then bubbled into the solution through a sparger having a centralpipe with eight medium porous plastic filter candles (Bel-Art Products, Pequamock, New Jersey) as the exit medium for increasing air-solution contact. The air supply for the sparger has a flow rate gauge and regulator with which the air flow is adjusted to give maximum aeration with minimum solution loss through foaming. The aeration is continued until the balancing developing agent is destroyed, which is indicated by testing a drop of solution on a thin layer chromatographic sheet and spraying with silver nitrate solution. If the spot turns black, there is developing agent remaining in solution. When a spot fails to turn black on spraying with silver nitrate, the developing agent has been completely destroyed.

After the balancing agent is destroyed, a centrifuge is utilized to separate the precipitated oxidized residues of the balancing developing agent. The solution is then poured into a 500 liter tank and diluted about five fold with water at l30 F. The solution is then pumped at about 2 liters per minute into a 35 liter slurry tank which is fitted with a mechanical stirrer. CO is added to the slurry tank at about 8 cubic feet per hour to maintain the pH at about 7.5 and precipitate the coupler. The coupler-containing overflow from the slurry tank is piped to a centrifuge to separate the precipitate from the solution. The coupler is washed about one hour in hot F.) water. The coupler is then separated from the wash solution again using a centrifuge. The damp coupler is then taken from the centrifuge, placed in trays, and dried in an oven. About 6 kg. of 91% assay coupler are obtained.

EXAMPLE 2 The procedure according to Example 1 is followed except that the weight of the damp coupler-balancing developing agent used is about 1 kg.; appropriately smaller containers and quantities are utilized; the coupler solution is not diluted; and the reprecipitation step is accomplished by slow addition of 0.6 N sulfuric acid to the coupler solution with stirring until the solution reaches about pH 7 (about volume for volume addition). The slurry is then poured into a centrifuge, separated, and washed. The yield (percent) and purity of coupler is analogous to Example 1.

EXAMPLE 3 The procedure according to Example 2 is followed except that the color developing agent in the developer is 4 amino 3 methyl-N-iethyl-N-(fi-hydroxyethyl)aniline sulfate in lieu of that of Example 1. Results about the same as in Example 2 are obtained.

EXAMPLE 4 To a liter of used developer solution, costaining the color developing agent according to Example 3, about 1 g. 2,4-bis(benzenesulfonamido)phenol and about 1 g. N-(o-acetamido phenethyl)-l-hydroxy-2-naphthamide, is added to about 20 g. sodium sulfite. Air is then bubbled into the solution through a sparger for 30 minutes. The solution is then filtered, acid added as in Example 3, separated, and Washed. The coupler assay of the precipitated coupler increases from 52% (precipitation with no aeration) to 77% (precipitation with one-half hour aeration).

EXAMPLE 5 The procedure according to Example 4 is followed except that prior to aeration the coupler and balancing developing agent are precipitated with carbon dioxide and separated by centrifugation from the remaining developer solution. The precipitate having 57% coupler assay is taken up into solution having a pH of about 13.5 and then aerated. After 30 minutes aeration the coupler assay is 77% and after one hour is 82%.

EXAMPLE 6 A solution is prepared by dissolving 2,4-bis(benzenesulfonamido)phenol and N-(o-acetamido phenethyl)-1- hydroxy-Z-naphthamide in separate basic solutions, which are then combined to an adjusted volume of 1 liter (pH about 13). An analysis by standard chromatographic techniques indicates 16.4 g./l. of balancing developing agent and 73.6 g./l. of coupler. To a 500 ml. portion of this solution is added ml. of 30% hydrogen peroxide; the mixture is stirred for 20 minutes and after standing hours, the solution is analyzed for balancing developing agent. The concentration is reduced to about 9 g./l.

EXAMPLE 7 The proedure aucording to Example 6 is followed except that ml. of 30% hydrogen peroxide is used in lieu of the 10 ml. in Example 6. The balancing developing agent concentration is reduced to less than 2.3 g./l. While the coupler concentration is still about 70.5 g./l.

EXAMPLE 8 The procedure according to Example 6 is followed except that in place of the hydrogen peroxide there is included about 20 g./l. potassium persulfate. The balancing developing agent concentration is reduced to about 7.7 g./l.

EXAMPLE 9 The procedure according to Example 6 is followed except that in place of the hydrogen peroxide there is included about 40 g./l. potassium persulfate. The balancing developing agent concentration is reduced to less than about 1.9 g./l.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A method for separating N-(o-acetamidophenethyl)-1-hydroxy-2naphthamide coupler from a solution comprising 2,4-bis(benzenesulfonamido)phenol competing agent, water, said coupler, and suflicient alkali to maintain said coupler and said competing developing agent in solution, said method comprising:

(a) contacting said solution with an oxidizing agent whereby said competing developing agent is converted to base insoluble and/or acid soluble oxidation products;

(b) treating said solution to assure that the solution is substantially free from suspended solids;

(c) lowering the pH of the solution to precipitate said coupler; and

(d) separating said precipitate from the remaining solution.

2. The method according to claim 1 wherein said oxidizing agent is oxygen.

3. The method according to claim 1 wherein said oxidizing agent is oxygen supplied by aeration of the solution.

4. The method according to claim 1 wherein said solution has a pH in excess of 10.

5. A method for recovering n-(O-acetamido phenethyl)- 1 hydroxy 2 napthamide coupler from a used developer solution which contains color developing agent, 2,4-bis(benzenesulfonamido)phenol competing developing agent, as a said coupler water, and at least sufficient alkali to maintain said components in solution, said method comprising:

(a) contacting said solution with an oxidizing agent whereby said competing developing agent is converted to base insoluble and/or acid soluble oxidation products;

(b) treating said solution to remove the solids which may be present after step (a);

(c) lowering the pH of the solution to precipitate the coupler; and

(d) separating said precipitate from the remaining solution.

6. The method according to claim 5 further including prior to step (a) the steps comprising.

(i) lowering the pH of the solution whereby said coupler and said competing developing agent precip itate from the solution;

(ii) separating the precipitate from the remaining solution; and

(iii) redissolving the precipitate in aqueous alkali.

7. The method according to claim 5 wherein said treating of step (b) comprises filtering said solution.

8. The method according to claim 5 wherein said step (d) comprises filtering to separate said precipitate from the remaining solution.

9. The method according to claim 5 wherein said solution has a pH of at least 10 and said method comprises:

(i) lowering the pH of the solution by the addition of carbon dioxide to precipitate said coupler and said competing developing agent;

(ii) separating the precipitate from the solution;

(ii) washing the precipitate;

(iii) redissolving the precipitate in a solution having a pH in excess of about 12.

(iv) adding sulfite to said solution;

(a) contacting said solution with oxygen supplied by aeration whereby said competing developing agent is converted to acid soluble oxidation products and/or products which are insoluble at pH in excess of 12;

(b) separating solids from the solution;

(c) lowering the pH of the solution by the addition of carbon dioxide to precipitate the coupler;

(d) separating the precipitate from the remaining solution; and

(e) washing the precipitate.

References Cited UNITED STATES PATENTS 8/1965 Anselm et al. 260559 R 7/1969 Anselm et al. 260562 A US. Cl. X.R. 9655 

